4,4'-thiobis(6-t-butyl-m-cresol) (hereinafter also identified as TBC) is a highly effective antioxidant for various polymers, especially polyolefins. Under most conditions, TBC confers satisfactorily long-term oxidation resistance to polyolefins, and it has been recently found that under some conditions, certain polymeric forms of TBC provide even longer-term oxidation resistance for polyolefins. See U.S. Pat. Nos. 3,986,981 issued Oct. 19, 1976 to B. J. Lyons.
It has heretofore been known to polymerize other thiobisphenols with elimination of the sulfur link to product polyphenylene ethers which, in general, do not have the antioxidant effectiveness of the thiobisphenol monomer. For instance, U.S. Pat. No. 3,133,899 issued May 19, 1964 to J. Kwiatek et al. discloses preparation of polyaryl ethers by oxidative coupling of 2,6-disubstituted thiobisphenols accomplished by contacting the monomer with a free oxygen-containing gas in an organic solvent such a pyridine, and in the presence of a copper chloride catalyst. During the reaction, the sulfur is eliminated from the monomer and a sulfur-free, linear polyphenylene ether is obtained.
U.S. Pat. Nos. 3,306,874 and 3,306,875 issued Feb. 28, 1967 to A. Hay disclose preparation of polyphenylene ethers by polymerization of 2,6-disubstituted phenols in the presence of oxygen and a copper salt/amine complex catalyst. The reaction occurs between the dehydrogenated oxygen atom of one phenol and the dehydrogenated para-situated carbon atom of a second phenol to form the polyether product.
U.S. Pat. No. 3,749,693 issued July 31, 1973 to G. Cooper also discloses preparation of polyphenylene ethers by oxidizing 2,6-disubstituted phenols in the presence of a copper salt/amine complex catalyst.
As distinguished from the aforementioned process in which polymeric products are obtained from thiobisphenols with elimination of sulfur from the polymer chain, it is an object of this invention to provide a process by which TBC can be polymerized without the elimination of its sulfur atom, e.g. to provide polymers such as those described in U.S. Pat. No. 3,986,981. Another object is to provide such a process which proceeds relatively rapidly and with an attractive yield of the polymeric product. Other objects will be apparent from the following disclosure.